Lee Corbett (Biology) Middlebury College

In 1720 a freshwater swamp in Williamsburg, VA was flooded to create a millpond, and a subsequent 1 m rise in lake level was completed in 1930. Throughout the impoundment's history, significant development has occurred in the surrounding watershed, causing changes in runoff patterns and water quality. To study the evolution of sediment and algal production in Lake Matoaka, three cores were taken from different areas and analyzed for carbon to nitrogen ratios and total biogenic silica. Both variables show high algae concentrations in the swamp sediment, followed by a drastic decrease that marks the creation of the lake in 1720. A long, steady decreasing trend follows, suggesting a gradual degradation of water clarity and the resulting decrease in benthic algae populations. Poor water clarity may have been driven by runoff from deforestation of the watershed. A sudden increase of aquatic organic material marks the 1930 raise of water level, indicating the growth of algal blooms in the water column. The continued increase of algae populations since 1930 may be stimulated by runoff containing fertilizers and sewage from increased development within the watershed. These trends demonstrate that the composition of organic material in lake sediment reflects human impacts on the health of the watershed.